Metapopulation dynamics of wild dogs in South Africa

The survival of the African wild dog, whose numbers have been calculated at between 3 000 and 5000, has long been under threat. Photo by Roger de la Harpe, via showme.co.za

Background

Ideally, species should be protected in areas large enough to allow for natural demographic and genetic processes. However, in realty, species often occur in small and isolated patches of suitable habitat embedded in human-dominated landscapes. In metapopulation ecology, landscapes are viewed as networks of habitat patches (fragments) in which species occur as discrete local populations connected by migration. The dynamics of such a metapopulation is characterised by (asynchronous) local extinction and recolonisation events.

However, human modification of the landscape between habitat patches, the so-called matrix, often prevents migration. While establishing ‘corridors’ through the matrix may allow dispersing individuals to move from one habitat patch to another, this is often problematic in practice. This raises the question of how metapopulation viability can be achieved in fragmented landscapes with limited natural dispersal among isolated habitat patches. Here, we provide one possible approach for endangered African wild dogs (Lycaon pictus).

Managed metapopulation concept

In South Africa, the conservation strategy followed for wild dogs has lead to the establishment of a metapopulation composed of a number of discrete local populations within several small protected areas. These isolated populations are generally too small to persist on their own, and thus extinction-prone. Furthermore, although wild dogs can disperse over considerable distances, the level of natural dispersal seems insufficient to ensure metapopulation viability, which is largely due to human intolerance of wild dogs roaming in the matrix.

This metapopulation is thus managed in that the process of dispersal is mimicked by intermittently translocating wild dogs among protected areas. In terms of classic metapopulation dynamics, the populations occupying discrete habitat patches are indeed locally unstable but migration among isolated fragments is facilitated by human transfer, thereby preventing local extinction. This conservation strategy has been successful in that it has lead to the creation of a managed metapopulation comprising several small and fenced human-colonised sites.

Outlook

Despite being undoubtedly successful, the South African conservation strategy for wild dogs raises some awkward issues. Do we want to continue translocating wild dogs in perpetuity in order to mimic dispersal, or do we want levels of natural dispersal to raise sufficiently to achieve metapopulation viability? If we opt for the latter, promoting natural dispersal of wild dogs outside protected areas will be decisive, a goal that we will not achieve by continuously persecuting animals roaming in the matrix between protected areas containing wild dogs.

For wild dogs in South Africa, the crucial question is whether connecting protected areas (e.g. via corridors) is actually realistic on a spatial scale necessary to sustain a viable metapopulation. Natural metapopulation dynamics is certainly preferable, the feasibility of which needs to be assessed with spatially explicit metapopulation models. This approach hopefully provides a template for metapopulation management of other endangered species living in equally isolated habitat patches in increasingly human-fragmented landscapes.